If you follow these pages you will have already seen more than one mention of VirtualBox, one of the alternatives of virtualization More popular. And an essential question to be able to use it in the most complete way possible is that of install Guest Additions.
It is a complement that allows us a stronger integration between the host operating system and those that we use as guests, so that from the latter we can access the shared folders of the 'host' platform, among several other benefits.
Let's see then, how to install Guest Additions in Ubuntu, this being the virtual machine platform. To begin with, we start the virtual machine and then execute:
sudo apt-get update && sudo apt-get dist-upgrade
Then, we reboot the system, and then we run Virtualbox. Once there, we go to the toolbar: 'Devices → Install Guest Additions'. When doing so, we will be asked if we want to run a tool that will be launched directly from 'VBOXADDITIONS_4.2.6_82870' or something similar (depending on the version we are running). We accept (by clicking on 'Run'.
Afterwards, we are in a position to install Virtualbox extension packs, which add support for USB 2.0 devices, for RDP and PXE among other things. To do this we just have to go to the Virtualbox download page, download and then go to File → Preferences → Extensions, and click on the pack that we have downloaded.
More information - How to install Virtualbox on Debian and Ubuntu (and derivatives)